U.S. patent application number 11/736897 was filed with the patent office on 2008-05-22 for high frequency connector-less charging scheme.
This patent application is currently assigned to INTERSIL AMERICAS INC.. Invention is credited to FRED GREENFELD, GURUPRAKASH RADHAKRISHNAN.
Application Number | 20080116846 11/736897 |
Document ID | / |
Family ID | 39416264 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080116846 |
Kind Code |
A1 |
GREENFELD; FRED ; et
al. |
May 22, 2008 |
HIGH FREQUENCY CONNECTOR-LESS CHARGING SCHEME
Abstract
A connector-less charging circuit includes a transformer having
a primary side associated with a secondary side. A primary switch
is responsive to a control signal for connecting the transformer to
ground during a first portion of a duty cycle, and disconnecting
the transformer from ground during the second portion of the duty
cycle. An active clamp circuit connects to the primary side of the
transformer for recycling leakage energy from the transformer back
to the source responsive to the control signal during the second
portion of the duty cycle. A PWM controller generates the control
signal to both the active clamp circuit and the primary switch.
Inventors: |
GREENFELD; FRED; (NEDERLAND,
CO) ; RADHAKRISHNAN; GURUPRAKASH; (MELBOURNE,
FL) |
Correspondence
Address: |
HOWISON & ARNOTT, L.L.P
P.O. BOX 741715
DALLAS
TX
75374-1715
US
|
Assignee: |
INTERSIL AMERICAS INC.
MILPITAS
CA
|
Family ID: |
39416264 |
Appl. No.: |
11/736897 |
Filed: |
April 18, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60821505 |
Aug 4, 2006 |
|
|
|
Current U.S.
Class: |
320/108 ;
320/115 |
Current CPC
Class: |
H02J 7/025 20130101;
H02J 50/10 20160201; H02J 7/00 20130101 |
Class at
Publication: |
320/108 ;
320/115 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Claims
1 A connector-less charging circuit, comprising: a transformer
having a primary side for coupling a charging voltage to a
secondary side of the transformer, the primary side removably
associated with the secondary side; a primary switch responsive to
a control signal for connecting the transformer to ground during a
first portion of a duty cycle and disconnecting the transformer
from ground during a second portion of the duty cycle; an active
clamp circuit connected to the primary side of the transformer for
recycling leakage energy from the transformer back to the source
responsive to the control signal during the second portion of the
duty cycle; and a PWM controller for generating the control
signal.
2. The connector-less charging circuit of claim 1, wherein the
secondary side of the transformer comprises an asymmetrically
wrapped center tapped transformer.
3. The connector-less charging circuit of claim 2, further
including an output capacitor, wherein the output capacitor is
peaked charged by a first portion of the asymmetrically wrapped
center tapped transformer during the first portion of the duty
cycle and by a second portion of the asymmetrically wound center
tapped transformer during the second portion of the duty cycle.
4. The connector-less charging circuit of claim 1, wherein the
active clamp circuit further includes: a clamp capacitor; and a
p-channel transistor switch for connecting the clamp capacitor to
ground during the second portion of the duty cycle.
5. The connector-less charging circuit of claim 1, wherein the PWM
controller comprises a single-ended controller.
6. The connector-less charging circuit of claim 1, wherein circuit
operates at a frequency of at least 300 kilohertz.
7. The connector-less charging circuit of claim 1, wherein the
primary side of the transformer further comprises a core half with
a winding wrapped around one leg of the core half.
8. The connector-less charging circuit of claim 7, wherein the
secondary side of the transformer further comprises: two sets of
windings configured to slide over the primary side of the
transformer; and wherein the core-winding combination of the
primary side of the transformer is inserted concentrically within
the secondary windings to enable electrical coupling between the
primary side and the secondary side.
9. The connector-less charging circuit of claim 8, wherein an
amount of coupling is responsive to an airgap between the primary
core and secondary core halves.
10. A connector-less charging circuit, comprising: a transformer
having a primary side for coupling a charging voltage to a
secondary side of the transformer, the primary side removably
associated with the secondary, wherein the secondary side of the
transformer comprises an asymmetrically wrapped center tapped
transformer; a primary switch responsive to a control signal for
connecting the transformer to ground during a first portion of a
duty cycle and disconnecting the transformer from ground during a
second portion of the duty cycle; an active clamp circuit connected
to the primary side of the transformer for recycling leakage energy
from the transformer back to the source responsive to the control
signal during the second portion of the duty cycle, wherein the
active clamp circuit further includes: a clamp capacitor; and a
p-channel transistor switch for connecting the clamp capacitor to
ground during the second portion of the duty cycle; and a PWM
controller for generating the control signal.
11. The connector-less charging circuit of claim 10, further
including an output capacitor, wherein the output capacitor is peak
charged by a first portion of the asymmetrically wrapped center
tapped transformer during the first portion of the duty cycle and
by a second portion of the asymmetrically wrapped center tapped
transformer during the second portion of the duty cycle.
12. The connector-less charging circuit of claim 10, wherein the
PWM controller comprises a single-ended controller.
13. The connector-less charging circuit of claim 10, wherein
circuit operates at a frequency of at least 300 kilohertz.
14. The connector-less charging circuit of claim 10, wherein the
primary side of the transformer further comprises: a core having at
least one leg; and a winding wrapped around the at least one
leg.
15. The connector-less charging circuit of claim 14, wherein the
secondary side of the transformer further comprises: two sets of
windings configured to slide over the primary side of the
transformer; and wherein the core-winding combination of the
primary side of the transformer is inserted concentrically within
the secondary windings to enable electrical coupling between the
primary side and the secondary side.
16. A system, comprising: a charging base station defining a
charging bay therein; a portable electronic device configured to
fit within the charging bay of the charging base station; charging
circuitry for providing a charging voltage to the portable
electronic device in the charging bay, the charging circuitry
comprising: a transformer having a primary side within the charging
base station for coupling the charging voltage to a secondary side
of the transformer within the portable electronic device, the
primary side removably associated with the secondary; a primary
switch within the charging base station responsive to a control
signal for connecting the transformer to ground during a first
portion of a duty cycle and disconnecting the transformer from
ground during a second portion of the duty cycle; an active clamp
circuit connected to the primary side of the transformer within the
charging base station for recycling leakage energy from the
transformer back to the source responsive to the control signal
during the second portion of the duty cycle; and a PWM within the
charging base station controller for generating the control
signal.
17. The system of claim 16, wherein the secondary side of the
transformer within the portable electronic device comprises an
asymmetrically wrapped center tapped transformer.
18. The system of claim 17, further including an output capacitor
within the portable electronic device, wherein the output capacitor
is peak charged by a first portion of the asymmetrically wrapped
center tapped transformer during the first portion of the duty
cycle and by a second portion of the asymmetrically wrapped center
tapped transformer during the second portion of the duty cycle.
19. The system of claim 16, wherein the active clamp circuit
further includes: a clamp capacitor; and a p-channel transistor
switch for connecting the clamp capacitor to ground during the
first portion of the duty cycle.
20. The system of claim 16, wherein the PWM controller comprises a
single-ended controller.
21. The system of claim 16, wherein system operates at a frequency
of at least 300 kilohertz.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a non-provisional of U.S. application
Ser. No. 60/821,505, entitled "HIGH FREQUENCY CONNECTOR-LESS
CHARGING SCHEME", filed on Aug. 4, 2006.
TECHNICAL FIELD
[0002] This invention is related to the charging of portable
electronic devices, and more particularly, to a system and method
for connector-less charging of portable electronic devices.
BACKGROUND
[0003] The growing number of portable electronic devices that are
used by individuals such as wireless headsets, PDA's, cell phones,
Ipod's, MP3 players, etc., have increased the need for varying
methods to recharge these devices. Existing technologies normally
involve the use of a power cord that is plugged into the portable
electronic device via some type of connector, and the power cord is
plugged into a wall socket to charge the batteries of the device.
This, of course, requires a certain amount of time to connect the
portable electronic device to the power cord.
[0004] Devices such as an electric toothbrush have used
connector-less charging methods by using a low frequency (line
frequency) transformer to couple the primary and secondary sides of
the transformer. Large spacings between the transformer, as
dictated by the application, cause poor coupling between the
primary and secondary sides, resulting in large leakage
inductances. As a result, present day solutions use low frequency
transformers to minimize the amount of leakage energy. The low
frequency of operation generally makes the connector-less chargers
fairly large for the amount of power they can transfer. These types
of solutions are not effective with the higher frequencies involved
in the charging of a portable electronic devices such as those
mentioned above. Thus, some system and method for providing a
connector-less charging connection for a portable electronic device
is desired.
SUMMARY
[0005] The present invention, as disclosed and described herein,
comprises, in one embodiment thereof, a connector-less charging
circuit that includes a transformer having a primary side for
coupling a charging voltage to a secondary side of the transformer.
The primary side of the transformer is removably associated with
the secondary side of the transformer. A primary switch is
responsive to a control signal for connecting the transformer to
ground during a first portion of a duty cycle and for disconnecting
the transformer from ground during a second portion of the duty
cycle. An active clamp circuit connected to the primary side of the
transformer recycles leakage energy from the transformer back to
the source responsive to the control signal during the second
portion of the duty cycle. The control signal is generated by a PWM
controller.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
description taken in conjunction with the accompanying Drawings in
which:
[0007] FIG. 1 is a block diagram of a connector-less charging
circuit;
[0008] FIG. 2 is a schematic diagram of one embodiment of the
connector-less charging circuit of FIG. 1;
[0009] FIG. 3 is a schematic diagram of the embodiment of FIG. 2
illustrating the active clamp and asymmetrically wound
center-tapped secondary; and
[0010] FIG. 4 illustrates the circuit of FIG. 3 in a first state of
operation;
[0011] FIG. 5 illustrates the circuit of FIG. 3 in second state of
operation;
[0012] FIG. 6 is a typical illustration of the drain-to-source
voltage of the primary switching transistor versus time; and
[0013] FIG. 7 illustrates the physical implementation of the
transformer of the circuit of FIG. 2.
DETAILED DESCRIPTION
[0014] Referring now to the drawings, wherein like reference
numbers are used herein to designate like elements throughout the
various views, embodiments of the present invention are illustrated
and described, and other possible embodiments of the present
invention are described. The figures are not necessarily drawn to
scale, and in some instances the drawings have been exaggerated
and/or simplified in places for illustrative purposes only. One of
ordinary skill in the art will appreciate the many possible
applications and variations of the present invention based on the
following examples of possible embodiments of the present
invention.
[0015] Referring now to FIG. 1, there is illustrated a block
diagram of a connector-less charging system according to the
present disclosure. The configuration enables for the use of
high-frequency charging in a connector-less charging technique
using the modified DC to DC converter illustrated in FIG. 1. The
higher frequency enables a smaller transformer 107 to be used. The
proposed implementation operates at a switching frequency of at
least 300 kHz enabling power components of a smaller size to be
utilized. This provides for a manner of charging portable electric
devices that operate within a provided DC input voltage range.
[0016] A first group of components associated with a transformer
primary 108 are located in a charging base station that defines a
charging bay for a portable electronic device. The DC input is
placed across input terminals 102 and 104 to an input filter
capacitor 106. The input filter capacitor 106 is connected to the
transformer primary 108 of the transformer 107. The transformer
primary 108 is separated from the transformer secondary 110 by an
air gap, depending on a combination of the case thicknesses, and
how tightly the portable electronic device is cradled in the
charging bay. Connected to the transformer primary is a clamp
capacitor 112 and an N-channel FET transistor 116, which comprises
the primary switching transistor of the circuit. A P-channel FET
transistor 114 actively resets the core of the transformer 107. The
N-channel FET transistor 116 is connected to a current sense
circuit 118, and the P-channel FET transistor 114 is connected to
receive a drive signal from a PWM controller 120 through a charge
pump inverter 122. The PWM controller 120 additionally provides
control drive signals to the N-channel FET transistor 116. The PWM
controller comprises a single-ended PWM controller. The combination
of the P-channel FET transistor 114, N-channel FET transistor 116
and clamp capacitor 112 enables the circuit to utilize the benefit
of an active clamp forward on the transformer primary 108 such that
leakage and magnetizing energy are recycled back to the source. The
active clamp forward on the transformer primary 108 recycles most
of the leakage energy back to the source and provides an ideal
reset mechanism for efficiency of operation.
[0017] The other portion of the transformer 107 consists of the
transformer secondary 110. The transformer secondary 110 and all
associated components are located within the portable electronic
device while the components described previously associated with
the transformer primary are associated with some type of base
station unit having a charging bay for the electronic device.
Connected to the transformer secondary 110 are two rectifiers 124
and 126 to rectify the signals from the transformer secondary 110.
The rectifiers 124 and 126 are each connected to an output
capacitor 128. The output capacitor 128 is connected across the
output node 130 and a center-tap ground 132 and is peaked charged
by the transformer secondary 110.
[0018] The use of peak charging of the output capacitor enables the
design to eliminate the output inductor. Elimination of the output
inductor improves load regulation particularly at light loads.
Given the requirements of the application, the primary and
secondary circuits are separable sections. The converter produces
an unregulated output and does not require monitoring of the output
voltage for regulation. There will be no feedback, thereby allowing
open-loop operation. The transformer secondary 110 comprises an
asymmetrically configured center-tapped transformer. The open loop
operation of the circuit means that the converter operates at its
maximum duty cycle which is limited only by the voltage stress on
the primary transistor 116. The embodiment presented here limits
the duty cycle to a maximum of 50%, but is practically limited to
approximately 47%. The turns ratio of the asymmetrical secondary
windings need to be selected to account for the duty cycle of
primary transistor 116. The voltages developed across each
secondary winding must be equal to the desired output voltage (plus
losses) when they are conducting since the output capacitor 128 is
peak charged. By asymmetrically winding the center-tapped
transformer secondary 110, the voltage applied to the output
capacitor 128 during the on time and during off time can be made
equal. By having the center-tapped transformer asymmetrically wound
in an appropriate manner, the peak charging of the capacitor 128
will be roughly equal during each portion of the switching cycle.
No inductor is used in the transformer secondary to allow open loop
regulation under light and no load conditions.
[0019] Referring now to FIG. 2, there is illustrated a schematic
diagram of one embodiment of the circuit of FIG. 1. The input
voltage is applied across nodes 202 and 204 across a capacitor 206.
The capacitor 206 comprises the capacitor filter 106 described
previously with respect FIG. 1. A first side of the transformer
primary of transformer 208 is connected to node 202. The second
side of the transformer primary of transformer 208 is connected to
node 210. As described previously with respect to FIG. 1, the node
210 is connected to a clamp capacitor 242 and to an N-channel FET
transistor 212, which comprises the primary switching transistor.
The P-channel FET transistor 226 is connected to the primary
circuit between nodes 230 and node 231. The charge pump inverter
consists of diodes 234 and 236, resistors 240 and 241, and
capacitor 239. Diode 234 has its anode connected to node 232 and
its cathode connected to node 231. Diode 236 has its anode
connected to node 238 and its cathode connected to node 232. A
resistor 240 is in parallel with the diode 236 between nodes 232
and 238. The gates of N-channel transistor 212 and P-channel
transistor 226 each receive control signals form a PWM controller
218. The PWM controller 218, in one implementation, may comprise
the ISL 6401 controller manufactured by Intersil, Inc., which is a
single-ended controller. However, it would be realized by one
skilled in the art, that other types of PWM controllers may be
utilized to produce a control signal to the transistors 212 and 226
in a desired manner.
[0020] The connection between the gate of transistor 212 and the
PWM controller 218 includes a resistor 220 connected between the
gate node 216 of the transistor 212 and the output node 222 of the
PWM controller 218. A diode 224 is connected in parallel with the
resistor 220, having its anode connected to node 216 and its
cathode connected to node 222. The control path between the gate of
transistor 226 and the control output node 222 of the PWM
controller 218 includes the charge pump as described previously
consisting of diodes 234 and 236, resistors 240 and 241, and
capacitor 239. A resistor 244 is connected between node 214 and
node 246. Node 246 is also connected to the PWM controller 218. A
capacitor 248 is connected between node 246 and ground. A capacitor
250 is connected between node 202 and ground. A resistor 252 is
connected between node 202 and the SD input of the PWM controller
218. Node 246 is connected to the CS input of the PWM controller
218. A capacitor 254 is connected between the CT input of the PWM
controller 218 and ground. A capacitor 256 is connected between the
COMP input and node 258. The FB input of the PWM controller 218 is
also connected to node 258. A resistor 260 is connected between
node 258 and ground.
[0021] The transformer 208 is split along line 262 such that the
remaining components described herein would be located in the
portable electronic device that is being charged by the
connector-less charging system. The portions of the circuit
previously described would be associated with the base-station
charging unit. The secondary of the transformer 208 consists of an
asymmetrically wrapped center-tapped transformer. A first end of
the transformer secondary is connected to node 264. The second end
of the secondary of transformer 208 is connected to node 266. The
center-tapped node of the secondary of the transformer is at node
268. The rectification described previously with respect to FIG. 1
is performed by diodes 270 and 274. Diode 270 has its anode
connected to node 264 and its cathode connected to node 272. Diode
274 has its cathode connected to node 272 and its anode connected
to node 266 on the second side of the secondary of the transformer
208. A parallel combination of capacitors 276 and 278 connected
between node 272 and the center-tap node 268 of the secondary of
transformer 208 comprise the output capacitance of the circuit.
Node 272 provides the output voltage across the capacitors 276 and
278, and node 268 provides the center-tap ground of the
circuit.
[0022] The implementation illustrated in FIGS. 1 and 2 enables the
use of a DC to DC converter at high frequencies of approximately
300 kH in a connector-less charger. The specific topology utilizes
the key benefits of an active clamp forward on the transformer
primary by recycling most of the leakage and magnetizing energy
back to the source using the combination of the capacitor 242 and
P-channel transistor 226 under the control of the PWM controller
218. Additional benefits are achieved on the secondary of the
transformer utilizing an asymmetrically configured center-tapped
transformer, rectification using diodes 270 and 274, and peak
charging an output capacitor consisting of capacitors 276 and 278.
No secondary inductor is used. The output is achieved by peak
charging the output capacitors on the secondary side, and omitting
the inductor to allow for open loop operation. These benefits are
more fully illustrated in FIGS. 3-5.
[0023] Referring now to FIG. 3, there is illustrated a basic
schematic diagram of the connector-less charging circuit of the
present invention. The input voltage 302 is applied to the
transformer primary 304. The other end of the transformer primary
is connected to the primary switching N-channel transistor 306 and
the through the active clamp portion of the circuit consisting of
capacitor 308 and transistor 310 depending on the state of the
transistors. The center-tapped secondary transformer 312 is
inductively coupled to the transformer primary and provides an
output through the rectification circuit consisting of diodes 314
and 316 across output capacitor 318. The duty cycle of the control
signals applied to transistors 306 and 310 cause transistor 310 to
be off when transistor 306 is turned on, and for transistor 310 to
be turned on when transistor 306 is turned off.
[0024] Referring now to FIG. 4, there is illustrated the operation
of the circuit when the transistor 306 is turned on and transistor
310 is turned off. This state of operation causes the input voltage
to be coupled across the transformer from the primary side 304 to
the secondary side 312. In this state of operation, the diode 316
is reverse-bias and the upper portion of the secondary transformer
peak charges the capacitor 318 as illustrated. In this situation,
the first portion of the asymmetrically wrapped center-tapped
transformer 312 peak charges the capacitor 318.
[0025] Referring now to FIG. 5, there is illustrated the second
state of operation of the circuit wherein the transistor 306 is
turned off and transistor 310 is turned on. In this case, when the
primary side is turned off, the primary transformer 304 charges the
clamp capacitor 308, enabling the leakage energies to be funneled
back to the source as it discharges. On the secondary side, the
diode 314 is reverse-bias such that the capacitor 318 is peak
charge by the second portion of the center-tapped secondary
transformer 312 as illustrated.
[0026] Referring now to FIG. 6, there is illustrated the
drain-to-source voltage of the P-channel transistor 310 at various
points of operation of the circuitry. Once the magnetizing energy
with the transformer has fully been used to charge up the capacitor
308, the capacitor starts recycling this stored energy back to the
source 302. The p-channel transistor 310 provides a return path for
the flow of this energy. From time 0 to time T.sub.1 comprises the
"on" time of the transistor 306 when the drain-to-source voltage on
the P-channel transistor 310 is 0. When P-channel transistor 310 is
turned on and N-channel transistor 306 is turned off at time
T.sub.1, the drain-to-source voltage increases from T.sub.1 to
T.sub.2 as the inductor within transformer 304 charges the
capacitor 308. Once the capacitor 308 is completely charged at time
T.sub.2, P-channel transistor 310 enables the discharge of the
capacitor to ground from T.sub.2 to T.sub.3.
[0027] Referring now to FIG. 7, there are illustrated additional
improvements to the connector-less charging system that may be
achieved by the construction of the transformer 107. The
transformer 107 consists of a separable transformer primary portion
108 and transformer secondary portion 107. The transformer primary
108 includes a core 702 and winding 704 wound around it. The leg of
the core 702 around which the winding 704 is wrapped is inserted
within the concentrically wound secondary winding of the
transformer 110. The implementation of this scheme is represented,
but not limited to, the configuration discussed above.
[0028] This configuration maximizes the electromagnetic coupling
between the transformer primary 108 and transformer secondary 110.
This maximized coupling is key to achieving a reasonably good line
and load regulation despite a large air gap between the primary and
secondary. This air gap is dictated primarily by the wall thickness
of the portable electronic device charger and the portable
electronic device in order to properly insulate the transformers.
This thickness is assumed to be between 0.8 mm to 1 mm. While the
configuration of FIG. 7 illustrates that the core of the secondary
winding 110 is configured such that the primary winding 108 may be
inserted concentrically on the inside of the secondary winding 110,
in an alternative embodiment, the configuration could be altered
such that the secondary winding could be inserted within the
primary winding. This configuration maximizes the coupling between
the two halves of the transformer 208 to achieve good line and load
configuration despite the large air gap.
[0029] It will be appreciated by those skilled in the art having
the benefit of this disclosure that this invention provides an
improved connector-less charging scheme for charging portable
electronic devices, with the supply switching at frequencies of 300
kHz and above. It should be understood that the drawings and
detailed description herein are to be regarded in an illustrative
rather than a restrictive manner, and are not intended to limit the
invention to the particular forms and examples disclosed. On the
contrary, the invention includes any further modifications,
changes, rearrangements, substitutions, alternatives, design
choices, and embodiments apparent to those of ordinary skill in the
art, without departing from the spirit and scope of this invention,
as defined by the following claims. Thus, it is intended that the
following claims be interpreted to embrace all such further
modifications, changes, rearrangements, substitutions,
alternatives, design choices, and embodiments.
* * * * *